Yes, Camlobe,
Flying the PA30 and 39 are in my plans. My original question was brought about by the factor which barit1 has identified, that is the local AOA increase resulting from the flow from the upgoing propeller blade. A very well informed aerodynamisist friend suggested that it was desireable to have that higher local AOA more inboard that outboard, so that it's differential effect would be less if an engine quit. Thus the upgoing blade would have to be on the inboard side. All of the other information I have seen does support tips inward at the top though, as opposed to what my friend has suggested, I'm just keeping my mind open, and trying to observe everything I can.
The engine choice has been made for the modified aircraft, and it's nearly flight ready. My task is to evaluate it's handling for design compliance. I hope to fly the original version, with two right hand engines, to form a basis for comparison, though power increase will affect the observations. The original aircraft are getting hard to come by in flying condition, due to engine problems.
Cheers, Pilot DAR